I. Field of the Invention
The present invention relates generally to fuel control systems for internal combustion engines and, more particularly, an improved air/fuel sensor for gaseous fuel engines.
II. Description of the Prior Art
Internal combustion engines utilizing gaseous fuel, such as compressed natural gas, LNG and the like, are generally advantageous since gaseous fuels are generally clean burning fuels. As such, gaseous fuels for the most part generate less noxious emissions than other fuels and, as such, are able to meet increasingly rigorous governmental regulations.
In order to minimize noxious emissions for gaseous fuel engines, it is necessary to control the air/fuel ratio at or near a selected point, such as the stoichiometric point or a lean burn point. For example, the air/fuel ratio equals 17 at the stoichiometric point for compressed natural gas.
In order to monitor the air/fuel ratio in the previously known gaseous fuel engines, a lambda or oxygen sensor is positioned in the exhaust gas stream from the engine. The lambda sensor detects the presence of oxygen in the exhaust gas from the engine which, in turn, is representative of the air/fuel ratio for the engine.
One disadvantage of these previously known engines, however, is that the air/fuel ratio for the engine is only determined after the engine combustion has occurred. Consequently, there is a lag time between the time the combustion occurred and the time when adjustments can be made to the fuel supply for the engine in order to return the engine combustion to the selected point. This lag time disadvantageously increases undesirable engine emissions in the exhaust gas stream.